1. The Field of Invention
This invention relates to tensionable buckles and the like. Specifically, it pertains to an over-center tensionable buckle intended for use with wide, flat strapping material typically used with air cargo transportation.
2. The Prior Art
Devices for securing cargo during the transportation thereof are as old as drayage itself. Before the advent of air travel, the sole criteria by which such devices were evaluated was strength--was the device strong enough to hold the cargo in place during transportation. Although strength is still an important criteria (air cargo buckles designed for 13/4 inch straps must have a strength rating of 5,000 pounds), air travel and the energy crisis have added another criteria--weight. For example, currently it costs approximately $40.00 to fly one pound for one year on a Boeing 747 cargo airplane. When the countless hours such cargo planes fly is taken into consideration, the importance of weight reduction is apparent. Unfortunately, the mutual goals of strength and light weight are often evasive.
The prior art design for the typical air cargo tensionable buckle utilizes a lever and fulcrum concept to tension the strap. An "overcenter" rotatable handle portion is journaled between two side plates. The handle portion itself comprises two side panels, having, in the prior art design, three cross-pins between those side panels. The webbing material or strap is fed through and around these three pins, one of which acts as the fulcrum, the other two of which act as load pins. The handle portion is then rotated, pulling the slack out of the strapping material, and placing it under great tension.
In the prior art buckle, the load pins have a machined end of reduced diameter which extends through an appropriately sized aperture in the side panels of the handle portion of the buckle. The protruding end of the pin is staked to keep the pin in place. Unfortunately, this staking is not sufficient to keep the pins from rotating at the high torque loads typically developed in use. Of course, if the pins rotate, the webbing slips, allowing the straps to loosen, leading eventually to a shifting load which can cause serious unwanted consequences. Therefore, in the prior art buckle, three pins were used to withstand the loads encountered.
Each pin, of course, adds weight and cost to the buckle. Therefore, a buckle which could sustain similar loads without slipping with fewer pins would be a significant improvement in the art.